Rodrigo Marcos Silva Vieira’s mother asked his father not to go to work that night. Neighbors were warning of an informal police curfew in their poor neighborhood of Jardim Carumbé on the northern edge of São Paulo, and she thought better of defying it.

“But my father said there was nothing to worry about, and Rodrigo went to help him,” remembers Mr. Vieira’s sister Beatriz Silva Vieira. But around 1:30 am on Nov. 6, a motorbike with two men pulled up outside the small bar where Vieira and his father worked, and the passenger indiscriminately fired more than 20 shots into the establishment.

Vieira died in his father’s arms, and two others were also killed. “My mother cannot get out of bed with the pain,” says Ms. Vieira.

Ms. Vieira was too shocked to speculate on who was responsible for her brother’s death, but a group of indignant local friends say they have no doubt: “It was the police.”

“Today we cannot tell who is a bandit and who is a policeman,” says one, who out of fear asked not to be named, her view shared by other women comforting Ms. Vieira.

For several months, the slums of Brazil’s biggest city have been the scene of an unofficial war between the police and a shadowy gang that controls its underworld – the Primeiro Comando da Capital (PCC), or the First Command of the Capital.

The violence marks a backward step for a state that had succeeded in cutting its homicide rate by more than half in the past decade. And it risks tarnishing not only São Paulo’s human rights reputation but also the international image of Brazil’s financial capital just as the globe focuses on Brazil in the run-up to the 2014 World Cup.

The PCC is blamed for killing almost 100 police officers this year in what is the latest round of a rivalry war stretching back more than a decade. According to official records in May 2006 around 500 people, overwhelmingly civilian, died in 12 days after the gang attacked the police. The murder of dozens of officers provoked a spate of police killing civilians in poor neighborhoods in revenge, according to human rights groups.

The latest upsurge of violence seems to have been sparked by the killing of six gang members by São Paulo’s elite Rota police unit in May. The PCC has retaliated for that action by targeting police officers across the city and rogue elements within police units are countering this with further violence. But, again, civilians are bearing the brunt of the gunfire.

“What happens when a police officer is killed in São Paulo?” asks Guaracy Mingardi, one of Brazil’s leading criminologists. “If the case is not solved rapidly his colleagues will go out for revenge. This is why we have seen a revival in death squads after several years of decline.”

“Normally they kill those they consider suspects in one way or another,” Mr. Mingardi says. “Not suspects in the killing of their colleague but people they suspect of being criminals.”

30 percent rise in homicides

São Paulo’s police force is split between the uniformed Polícia Militar and the plain clothed investigative branch, the Polícia Civil. It is the Polícia Militar that has borne the brunt of the PCC’s attacks, and community leaders and human rights groups say the response by some of its officers has now gone beyond targeting criminals.

Whether in uniform or acting as plain-clothed death squads critics say the response now extends to any resident of neighborhoods with a strong PCC presence in often indiscriminate attacks that have left children as young as five dead.

The attack that killed Vieira was preceded by the murder of the son of an officer in the same neighborhood just hours before. The area was already saturated with police.

Residents told The Christian Science Monitor they saw officers removing bullet casings from the crime scene, something human rights groups say is a traditional practice when police try to cover for unsanctioned killers within their ranks. The local police trade union denied this, as well as the existence of police "death squads," and the state government declined repeated interview requests.

“The police just want to sow terror. The majority of those killed have no connection with crime. Their only crime was to live in crime-infested neighborhoods and these are people who have no choice about where they live,” says Gilberto Natalini, a member of São Paulo’s city council.

The violence has caused a 30 percent rise in the number of homicides in the city during the first ten months of the year. October was the bloodiest month yet with 176 deaths. It appears fear has gripped many regions on the poor periphery of the metropolis, with usually busy neighborhoods eerily quiet by 10:00 pm as people retreat indoors.

'Settling of accounts'

To be sure, not all the attacks on civilians are being carried out by police, say analysts. “There is also a settling of accounts taking place within the criminal underworld,” notes criminologist Mr. Mingardi.

And the police have sought to blame the indiscriminate attacks like the one that killed Vieira on the PCC and deny there are any death squads operating within their ranks.

But the force has a long history of harboring such groups, with officers convicted over the years of membership. The police response to PCC attacks in 2006 showed elements on the force are willing to target poor neighborhoods indiscriminately, say activists. “The information we have from police informants is that there is a death squad operating in every battalion of the Polícia Militar,” says Ivan Seixas of São Paulo’s Council for the Defense of Human Rights, Condepe.

With the crisis showing no sign of abating, and his approval rating plunging, the state’s Gov. Geraldo Alckmin was forced last month to sack his security secretary – a former policeman. Mr. Alckmin replaced him with Fernando Grella Vieira the state’s former attorney general, who has no background serving on the police force.

He immediately replaced the state’s top police officers and at his swearing in said the fight against organized crime had to combine “effective action by the state and unrestricted respect for human rights.”

“It is a positive start but now what is needed is concrete action,” says Professor Theodomiro Dias Neto, a Brazilian law professor and public security expert.